Thermosettable polymer or prepolymer prepared from heterocyclic material containing a nitrogen atom and carboxylic acid mono- or dianhydride

ABSTRACT

Thermosettable prepolymers are prepared by reacting (A) a heterocyclic material containing one or more rings and one nitrogen atom or a mixture of such materials wherein at least one of such materials contains at least two reactive substituent groups having at least one reactive hydrogen atom attached to a carbon atom which is attached to the ring such as 2,4,6-trimethyl pyridine; with (B) a cycloaliphatic or aromatic carboxylic acid mono- or dianhydride such as phthalic anhydride. These prepolymers or resins, can be homopolymerized without coreactants or copolymerized with N,N&#39;-bis-imides such as 1,1&#39;-(methylenedi-4,1-phenylene)-bismaleimide, to produce products, mat castings or composites having good mechanical and thermal properties.

This is a divisional of application Ser. No. 754,697, filed July 15,1985.

BACKGROUND OF THE INVENTION

The present invention concerns polymers prepared by reacting aheterocyclic material having one or more rings and 1 nitrogen atomtherein or mixtures thereof wherein at least one of such materialcontains at least 2 reactive substituent groups which have at least onehydrogen atom attached to a carbon atom which is attached to theheterocyclic ring with cycloaliphatic or aromatic carboxylic acid monoor dianhydrides.

It has been shown by Manly et al in J. Org. Chem., 1958, Vol. 23, pp.373-380 that indanediones can be prepared by reacting dimethylpyridineswith phthalic anhydride. He also stated that 2-methylpyridine reactedwith phthalic anhydride to form pyrophthalone.

Ogata in Japanese Pat. No. Sho 42(1967)-14468 prepared polymers thatmelt above 500° C. by reacting pyridine having methyl substituents withpyromellitic dianhydride.

The present invention provides polymers by the reaction of nitrogencontaining heterocycles having at least two reactive substituent groupswhich have at least one hydrogen atom attached to a carbon atom which isattached to the nitrogen-containing heterocyclic ring and one nitrogenatom with carboxylic acid mono or dianhydrides. Polymers with meltingpoints less than 300° C. can be obtained by the reaction of an aromaticheterocyclic material containing one nitrogen atom having such reactivesubstituent groups with dicarboxylic acid monoahydrides, or by thereaction of the aromatic nitrogen containing heterocycle having suchreactive substituent groups with a tetracarboxylic acid dianhydride orby addition of an aromatic nitrogen containing heterocycle having onesuch reactive substituent group or a dicarboxylic acid monoanhydride aschain terminators, or no catalyst, or limiting the reaction time, or anexcess of one of the reactants. These prepolymers can be homopolymerizedor copolymerized with a N,N'-bis-imide to give thermoset products withgood thermal properties as well as good physical properties.

For ease of processing the prepolymers as homopolymeric materials or ascopolymers with N,N'-bis-imides, it is desirable that the resin or resinmixture soften below 300° C., preferably below 200° C. For a resin toobtain its greatest utility it must be moldable. Molding of resins isconvenientally done at or about 200° C. or below. The resins producedfrom a nitrogen containing heterocycle with at least two reactivesubstituent groups and a tetracarboxylic acid dianhydride must havesoftening points at or about 200° C. or below in order to find theirgreatest use in forming composites of the homopolymer by solution or hotmelt prepregging, in blending with N,N'-bis-imides to form copolymers,or in forming composites from the N,N'-bis-imide copolymers. Theprepolymers discussed in this patent and the copolymers made by additionof N,N'-bis-imides all have softening points at or about 200° C. orbelow.

SUMMARY OF THE INVENTION

The present invention pertains to a polymer or prepolymer prepared byreacting (A) a heterocyclic material containing one or more rings andone nitrogen atom in the ring structure or mixture of any two or more ofsuch materials having at least one substituent group having at least onereactive hydrogen atom attached to a carbon atom which is attached tothe heterocyclic ring with the proviso that at least one of suchmaterials has at least two substituent groups having at least onereactive hydrogen atom attached to a carbon atom which is attached to aring; with (B) at least one cycloaliphatic or aromatic carboxylic acidmono- or dianhydride; wherein the reactants are employed in quantitieswhich provide a mole ratio of (A) to (B) of from about 0.25:1 to about4:1, preferably from about 0.8:1 to about 1.5:1.

Another aspect of the present invention pertains to a polymer orprepolymer prepared by reacting (A) a heterocyclic material containingone or more rings and one nitrogen atom in the ring structure or mixtureof any two or more of such materials having at least one reactivesubstituent group having at least one reactive hydrogen atom attached toa carbon atom which is attached to the heterocyclic ring with theproviso that at least one of such materials has at least two substituentgroups having at least one reactive hydrogen atom attached to a carbonatom which is attached to the heterocyclic ring; (B) at least onetetracarboxylic acid anhydride; and (C) at least one dicarboxylic acidmonoanhydride wherein the reactants are employed in quantities whichprovide a mole ratio of (A) to (B) to (C) of from about 0.25:1:0.1 toabout 4:1:4, preferably from about 0.8:1:0.5 to about 3:1:2.

A further aspect of the present invention pertains to the productsresulting from curing the aforementioned prepolymers by subjecting themto heat and pressure and/or copolymerization with a N,N'-bis-imide.

In order for the hydrogen atom of the substituent group which hydrogenatom is attached to a carbon atom attached to a ring to be reactive, thesubstituent group must be either ortho or para with respect to anitrogen atom.

DETAILED DESCRIPTION OF THE INVENTION

Any pyridine material which has at least two methyl, --CH(R²)₂ or --CH₂R² groups wherein each R² is independently a hydrocarbyl groupcontaining from 1 to about 20, preferably from 1 to about 10 carbonatoms attached to the ring on positions either ortho or para to the ringnitrogen can be employed herein.

The term hydrocarbyl as employed herein means any aliphatic,cycloaliphatic, aromatic, aryl substituted aliphatic or aliphaticsubstituted aromatic groups.

Particularly suitable as the heterocyclic material which can be employedherein include the pyridines such as, for example, 2,4-dimethylpyridine,2,6-dimethylpyridine, 2,4,6-trimethylpyridine,2,3,4,6-tetramethylpyridine, 4-ethyl-2,6-dimethylpyridine,2-ethyl-4,6-dimethylpyridine, 2,6-dimethyl-4-propylpyridine,2,5-diethyl-4,6-dimethylpyridine,2,6-dimethyl-4-(1-methylethyl)pyridine, 4-butyl-2,6-dimethylpyridine,2-butyl-3,4,6-trimethylpyridine, 2,6-dimethyl4-(2-methylpropyl)pyridine,2,4,6-triethylpyridine, 2,6-dimethyl-4-phenylpyridine,2,3,6-trimethyl-4-(2-methylpropyl)pyridine,2,6-dimethyl-3,4-pyridinediamine, 2,4,5-trimethyl-6-nitropyridine,2-chloro-4,6-dimethylpyridine, mixtures thereof and the like.2-Methylpyridine or 4-methylpyridine can be mixed or blended withpyridine having two or more reactive substituent groups to control themolecular weight of the prepolymer.

Other suitable aromatic nitrogen containing heterocycles which can beemployed herein include, quinolines and isoquinolines having two or morereactive substituent groups having at least one reactive hydrogen atomattached to a carbon atom which is attached to the heterocyclic ring.Such substituent groups include methyl, --CH(R²)₂ or --CH₂ R² wherein R²is as above defined.

Suitable quinolines include 2,4-dimethylquinoline, 2,4-diethylquinoline,2,4-dibenzylquinoline, 2-ethyl-4-benzylquinoline,2-ethyl-4-methylquinoline, mixtures thereof and the like.

Suitable isoquinolines include 1,3-dimethylisoquinoline,1,3-diethylisoquinoline, 1-ethyl-3-methylisoquinoline,1,3-dibenzylisoquinoline, 1-methyl-3-benzylisoquinoline, mixturesthereof and the like.

Molecular weight control of the prepolymer can be obtained by theaddition of an aromatic nitrogen containing heterocycle having onereactive substituent group which has at least one reactive hydrogen atomattached to a carbon atom which is attached to the ring to act as achain terminator in a mixture that contains an aromatic nitrogencontaining heterocycle having two or more reactive substituent groupswhich have at least one reactive hydrogen atom attached to a carbon atomwhich is attached to the ring. As an example, pyridines, quinolines orisoquinolines having one reactive substituent group which has at leastone hydrogen atom attached to a carbon atom which is attached to theheterocyclic ring can be mixed with an aromatic heterocycle containingone nitrogen having two or more reactive substituent groups which haveat least one reactive hydrogen atom attached to a carbon atom which isattached to the ring.

Suitable dicarboxylic acid monoahydrides which can be employed hereininclude, for example, those represented by the formula ##STR1## whereinR is a divalent radical such as, for example, ##STR2## wherein R¹ isalkyl, or one of the following: ##STR3## wherein R² is alkyl, aryl oraralkyl, or such groups containing substituents such as, for example,halogen, nitro or amino and where R³ is alkylene, oxygen, sulfur,oxyalkylene, polyoxyalkylene, or one of the following: ##STR4## whereinR⁴ and R⁵ are alkyl, aryl or such groups containing substituents suchas, for example, halogen, nitro or amino.

The preferred monoanhydrides are those in which the carbon atoms of thepair of carbonyl groups are directly attached to ortho carbon atoms inthe R group to provide a 5-member ring such as, for example, ##STR5##

Suitable such monoanhydrides include, for example, phthalic anhydride,3-nitrophthalic anhydride, tetraphenylphthalic anhydride,tetrachlorophthalic anhydride, tetrabromophthalic anhydride,hexahydro-4-methylphthalic anhydride, pyrazine-2,3-dicarboxylicanhydride, pyridine-2,3-dicarboxylic anhydride,quinoxaline-2,3-dicarboxylic anhydride, 2-phenylglutaric anhydride,isatoic anhydride, N-methyl isatoic anhydride, 5-chloroisatoicanhydride, 5-nitroisatoic anhydride, diphenic anhydride, 1,8-naphthalicanhydride, 4-chloro-1,8-naphthalic anhydride, 3-nitro-1,8-naphthalicanhydride, 3,4-coronenedicarboxylic anhydride,trans-1,2-cyclohexaneanhydride, 3,3-tetramethyleneglutaric anhydride,d,1-camphoric anhydride, mixtures thereof and the like.

Suitable tetracarboxylic acid dianhydrides which can be employed hereininclude, for example, those represented by the formula ##STR6## whereinR is a tetravalent aromatic radical such as, for example: ##STR7## whereR¹ is alkylene, oxygen, sulfur, oxyalkylene, polyoxyalkylene, or one ofthe following: ##STR8## wherein R² and R³ are alkyl, aryl or aralkyl, orsuch groups containing substituents such as, for example, halogen, nitroor amino.

Suitable such dianhydrides include, for example, pyromelliticdianhydride, benzene-1,2,3,4-tetracarboxylic dianhydride,pyridine-2,3,5,6-tetracarboxylic dianhydride,pyrazine-2,3,5,6-tetracarboxylic dianhydride,naphthalene-2,3,6,7-tetracarboxylic dianhydride,naphthalene-1,4,5,8-tetracarboxylic dianhydride,naphthalene-1,2,4,5-tetracarboxylic dianhydride,2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride,2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride,phenanthrene-1,8,9,10-tetracarboxylic dianhydride,3,4,9,10-perylenetetracarboxylic dianhydride,thiophene-2,3,4,5-tetracarboxylic anhydride,bis(3,4-dicarboxyphenyl)sulfone dianhydride,2,3,2',3'-benzophenonetetracarboxylic dianhydride,2,3,3',4'-benzophenonetetracarboxylic dianhydride,bis(2,3-dicarboxyphenyl)methane dianhydride,bis(3,4-dicarboxyphenyl)methane dianhydride,1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride,2,2-bis(2,3-dicarboxyphenyl)propane dianhydride,bis(3,4-dicarboxyphenyl)ether dianhydride,anthracene-2,3,6,7-tetracarboxylic dianhydride,fluorene-2,3,6,7-tetracarboxylic dianhydride,pyrene-1,2,7,8-tetracarboxylic dianhydride,quinoxaline-2,3,6,7-tetracarboxylic dianhydride,phenazine-2,3,7,8-tetracarboxylic dianhydride,1,1-bis(2,3-dicarboxy-5-oxyphenyl)ethane dianhydride, mixtures thereofand the like.

Tetracarboxylic acid dianhydrides can be mixed or blended withcycloaliphatic or aromatic monoanhydrides or mixtures of monoanhydridesas chain terminators to control molecular weight of the polymers.

If desired, the reaction can be conducted in the presence of a suitablesolvent, such as ketones, ethers, amides, acids, aromaticnitrogen-containing heterocycles containing no reactive substituentgroups (i.e. they do not have at least one hydrogen atom attached to acarbon atom which is attached to the heterocyclic ring), chlorinatedsolvents and the like. Particularly suitable solvents include,tetrahydrofuran, pyridine, acetic acid, N-methylpyrrolidone,N,N-dimethylacetamide, N,N-dimethylformamide,N,N-dimethylmethoxyacetamide, hexamethylphosphotriamide, mixturesthereof and the like.

The reaction temperature may vary depending upon the particularreactants employed. However, any temperature that allows completion ofthe reaction within a particularly desired time period is suitable.Usually, temperatures of from about 100° C. to about 250° C. are usedalthough lower and higher temperatures can be employed.

If desired, the reaction can also be conducted in the presence of acatalyst such as, for example, acids, Lewis acids, bases or salts.Particularly suitable acids include, for example, sulfuric,hydrochloric, glacial acetic or p-toluene-sulfonic acid. Particularlysuitable Lewis acids include boron trifluoride, aluminum trichloride andzinc chloride. Particularly suitable bases include, for example,hydroxides of alkali or alkaline earth metals or of quaternary ammonium.The use of such catalysts is not indispensable but it reduces the timerequired for the reaction. The amount is e.g. of from about 0.1 to about10 mole% with respect to the cycloaliphatic or aromatic carboxylic acidmono or dianhydride. If desirable, larger or lesser quantities can beemployed.

The reaction can also be accelerated by certain substances such asmethyl iodide, methyl sulfate, benzyl chloride etc., capable of formingwith the pyridinic base quaternary ammonium derivatives, such substancesbeing usable in catalytic amounts or higher proportions.

Addition of a dehydrating agent such as acetic anhydride,trifluoroacetic anhydride, trichloroacetic anhydride, propionicanhydride and the like can promote the reactions and its action can besufficient to render superfluous the incorporation of a catalyst. Thepreferred dehydrating medium is a mixture of glacial acetic acid andacetic anhydride. The acetic acid and acetic anhydride can be removed bydistillation, solvent extraction or solvent fractionation.

The reaction is usually conducted either under reduced pressure or in aninert atmosphere such as, for example, nitrogen, helium, neon, zenon,argon, mixtures thereof and the like.

Volatile emission during cure can be limited by subjecting thethermosettable prepolymers or resins of the present invention tosublimation, distillation or solvent extraction to remove reactants,catalyst and solvents. Suitable solvents for extraction include, forexample, alcohols, ketones, acetonitrile, ethers, hydrocarbons, esters,chlorinated solvents and the like. Particularly suitable solventsinclude acetonitrile, methanol, ethanol, acetone, mixtures thereof andthe like.

The thermosettable prepolymers or resins of the present invention can becured as is with the application of heat and pressure, or they can bedissolved in a suitable solvent or mixture of solvents and employed tosaturate various reinforcing materials so as to prepare compositestherefrom through the application of heat and pressure.

Suitable solvents which can be employed to saturate the variousreinforcing materials include, for example, ketones, acetates, alcohols,ethers, hydrocarbons and the like. Particularly suitable solventsinclude, for example, acetone, methylethylketone, ethyl acetate,methylene chloride, trichloroethylene, tetrahydrofuran, chlorobenzene,ethanol, n-propanol, N-methyl-pyrrolidone, dimethylformamide,dimethylacetamide, nitrobenzene, mixtures thereof and the like.

Suitable reinforcing materials include, for example, glass fibers,polyamide fiber, carbon or graphite fibers and the like in any form suchas, for example, matt, woven or fibrous form. Any synthetic or naturalfiber material can be employed as the reinforcing material.

The thermosettable prepolymers can be used according to variousconventional techniques applicable to thermosetting resins. Powderedprepolymers are especially adapted for shaping by pressure-molding, butthey can also be dissolved in a solvent or be employed in molten form.They can be used in the preparation of laminates or composites, films,coatings and the like.

The prepolymer is advantageously set by a thermal treatment at atemperature of from about 100° to about 300° C. If desired, the polymercan be compression molded at pressures up to about 100,000 psig (689MPa). Said polymer has a good thermal stability.

The prepolymer can be copolymerized with a N,N'-bis-imide of theformula: ##STR9## in which X represents a divalent radical containing acarbon-carbon double bond and A is a divalent radical having at least 2carbon atoms. Preferred N,N'-bis-imides which may be employed, include,for example 1,1'-(1,2-ethanediyl)bis-1H-pyrrole-2,5-dione; 1,1,'-(1,6-hexanediyl)bis-1H-pyrrole-2,5-dione;1,1'-(1,4-phenylene)bis-1H-pyrrole-2,5-dione;1,1'-(1,3-phenylene)bis-1H-pyrrole-2,5-dione;1,1'-(methylenedi-4,1-phenylene)bis-1H-pyrrole-2,5-dione(1,1'-(methylenedi-4,1-phenylene)bismaleimide);1,1'-(oxydi-4,1-phenylene)bis-1H-pyrrole-2,5-dione;1,1'-(sulfonyldi-4,1-phenylene)bis-1H-pyrrole-2,5-dione;1,1'-(methylenedi-4,1-cyclohexanediyl)bis-1H-pyrrole-2,5-dione;1,1'-[1,4-phenylenebis(methylene)]bis-1H-pyrrole-2,5-dione;1,1'-[(1,1-dimethyl-3-methylene-1,3-propanediyl)di-4,1-phenylene]bis-1H-pyrrole-2,5-dione;1,1'-[(1,3,3-trimethyl-1-propene-1,3-diyl)di-4,1-phenylene]bis-1H-pyrrole-2,5-dione;and Technochemie's H-795 resin. Technochemie's H-795 resin isrepresented by the generalized formula: ##STR10## where R is an aromaticring and X--R₁ --X is a Michael addition coupling group. Technochemie'sM-751 resin is a "eutectic" mixture of ##STR11## Many of these and othersuitable N,N'-bis-imides which can be employed herein are disclosed inU.S. Pat. No. 3,562,223 which is incorporated herein by reference.

The following examples are illustrative of the invention, but are not tobe construed as to limiting the scope thereof in any manner.

PREPARATION I Preparation of a Polyindanylpyridine Prepolymer

A solution of 200 g (1.65 moles) of 2,4,6-trimethylpyridine, 4 ml ofconcentrated H₂ SO₄, and 148 g (1.0 mole) of phthalic anhydride wasplaced in a 500 ml resin kettle equipped with a mechanical stirrer, N₂purge, thermometer, and a reflux condenser. The kettle was heated toreflux (170°-180° C.) by using IR lamps. The solution was stirred wellfor the 8 hours of reflux and then allowed to cool for 12 hours (43,200s) without stirring. The material left in the flask is a solid at roomtemperature. The volatiles (low molecular weight products and startingmaterials) can be removed from the crude product directly by placing itin a vacuum oven or by washing the sample with relatively low polaritysolvents (e.g. CH₂ Cl₂, acetone) or a mixture of these solvents. Theprepolymer recovered has a mp 155°-185° C. The melting point andmolecular weight of the prepolymer can be adjusted by the amount of timethe reaction is run initially or the length of time the material isB-staged.

PREPARATION II Preparation of a Polyindacenylpyridine Prepolymer

A solution of 182 g (1.5 moles) of 2,4,6-trimethylpyridine, 4 ml ofconcentrated H₂ SO₄, and 218 g (1.0 mole) of pyromellitic dianhydride,and 150 ml of DMF was placed in a 500 ml resin kettle equipped with amechanical stirrer, N₂ purge, thermometer, and a reflux condenser. Thekettle was heated to reflux (170°-180° C.) by using IR lamps. Thesolution was stirred well for the 8 hours (28,800 s) of reflux and thenallowed to cool for 12 hours (43,200 s) without stirring. The materialleft in the flask is a solid at room temperature. The low molecularweight products and starting materials were removed from the crudeproduct directly by placing it in a vacuum oven at 180° C. for 3 to 5hours. The melting point and molecular weight of the prepolymer can beadjusted by the amount of time the reaction is run initially or thelength of time the material is heated under vacuum. A melting point ofapproximately 180° C. is most desirable and is achieved with about 4hours (14,400 s) of heating under vacuum.

PREPARATION III Preparation of Polyindanylpyridine and BismaleimideCopolymer

A blend of 20 g of polyindanylpyridine prepolymer and 20 g of Compimide795* were mixed thoroughly and put into a glass dish. The dish was thenplaced into a vacuum oven that had been preheated to 160° C. The mixturewas heated under a full vacuum until the mixture was tacky (˜2 hours,7200 s). The material was cooled to room temperature and ground into afine powder. This copolymer can then be formed into a casting or moldedproduct at a temperature of approximately 177° C. by conventionalprocesses.

PREPARATION IV Preparation of Prepreg on Nextel* Woven Fabric UsingPolyindacenylpyridine

Fifteen grams of the polyindacenylpyridine and 4 g of DMF were addedtogether to give a solution that is 80 weight percent solids. Thesolution was then heated to 100° C. where the solution's viscosity waslow enough to be brushed onto the woven fabric mat. The mat was allowedto dry for 1 hour (3600 s) and then the resin containing solution wasadded to the reverse side. After air drying the mat was dry to the touchbut was still flexible. This prepreg can be fabricated with known artinto a composite.

PREPARATION V Preparation of Prepreg on Nextel Woven Fabric UsingPolyindanylpyridine

Ten grams of the polyindanylpyridine and 5 g of DMF were added togetherto give a solution that is 66 weight percent solids. The solution wasthen heated to 100° C. where the solution's viscosity was low enough tobe brushed onto the woven fabric mat. The mat was allowed to dry for 1hour (3600 s) and then the resin containing solution was added to thereverse side. After air drying the mat was dry to the touch but wasstill flexible. This prepreg can be fabricated with known art into acomposite.

PREPARATION VI Preparation of Polyindacenylpyridine and BismaleimideCopolymer

A blend of 20 g of polyindacenylpyridine prepolymer and 20 g ofCompimide 795* were mixed thoroughly and put into a glass dish. The dishwas then placed into a vacuum oven that had been preheated to 160° C.The mixture was heated under a full vacuum until the mixture was tacky(1-2 hours, 3600-7200 s). The material was cooled to room temperatureand ground into a fine powder. This copolymer can then be formed into acasting or molded product at a temperature of approximately 177° C. byconventional processes.

PREPARATION VII Preparation of Prepreg on Nextel Woven Fabric Using aCopolymer of Polyindanylpyridine and Bismaleimide

Fifteen grams of the polyindanylpyridine/bismaleimide copolymer and 4 gof DMF were added together to give a solution that is 80 weight percentsolids. The solution was then heated to 100° C. where the solution'sviscosity was low enough to be brushed onto the woven fabric mat. Themat was allowed to dry for 1 hour (3600 s) and then the resin containingsolution was added to the reverse side. After air drying the mat was dryto the touch but was still flexible. This prepreg can then be fabricatedwith known art into a composite.

PREPARATION VIII Preparation of Prepreg on Nextel Woven Fabric Using aCopolymer of Polyindacenylpyridine and Bismaleimide

Fifteen grams of the polyindacenylpyridine/bismaleimide copolymer and 4g of DMF were added together to give a solution that is 80 weightpercent solids. The solution was then heated to 100° C. where thesolution's viscosity was low enough to be brushed onto the woven fabricmat. The mat was allowed to dry for 1 hour (3600 s) and then the resincontaining solution was added to the reverse side. After air drying themat was dry to the touch but was still flexible. This prepreg can thenbe fabricated with known art into a composite.

EXAMPLE 1 Example of Polyindanylpyridine as a Neat Resin Molding

The polyindanylpyridine made in Preparation I was molded at 210° C.under 400 psi for 3 hours (10,800 s) and then 4 hours (14,400 s) at 215°C. Finally, the temperature was raised to 220° C. for 6 hours (21,600s). The cured material had a char yield in N₂ of 64% at 950° C., whichis indicative of high thermal stability.

EXAMPLE 2 Example of Polyindacenylpyridine as a Composite

The prepreg mat formed in Preparation IV was B-staged in a vacuum ovenat 175° C. under full vacuum for 45 minutes (2700 s) to remove thesolvent. The B-staged material was then pressed at 225° C. for 27 hours(97,200 s) under 500 psi (3447 kPa) pressure to give a composite withresin content of 50 weight percent loading. This composite had a Tg of230° C.

EXAMPLE 3 Example of Polyindanylpyridine as a Composite

The prepreg mat formed in Preparation V was B-staged in a vacuum oven at165° C. under full vacuum for 40 minutes (2400 s) to remove the solvent.The B-staged material was then pressed at 205° C. for 16 hours (57,600s) under 1000 psi (6895 kPa) pressure to give a composite with resincontent of 39 weight percent loading. This composite had a Tg of 190° C.

EXAMPLE 4 Example of Polyindacenylpyridine/Bismaleimide Copolymer as aNeat Resin Molding

The copolymer of polyindacenylpyridine/bismaleimide made in PreparationVI was molded at 185° C. under 2000 psi pressure for 10 hours (36,000 s)and then post cured for 30 minutes (1800 s) at 195° C. The curedmaterial had a char yield in N₂ of 62% at 950° C., which is indicativeof high thermal stability. This casting had a Tg of 268° C.

EXAMPLE 5 Example of Polyindanylpyridine/Bismaleimide Copolymer as aNeat Resin Molding

The copolymer of polyindanylpyridine/bismaleimide made in PreparationIII was molded at 205° C. under 2000 psi for 2 hours (7200 s) and then 6hours (21,600 s) at 215° C. Finally, the temperature was raised to 220°C. for 6 hours (21,600 s). The cured material had a char yield in N₂ of55% at 950° C., which is indicative of high thermal stability.

EXAMPLE 6 Example of Polyindacenylpyridine/Bismaleimide Copolymer as aComposite

The prepreg mat formed in Preparation VIII was B-staged in a vacuum ovenat 170° C. under full vacuum for 40 minutes (2400 s) to remove thesolvent. The B-staged material was then pressed at 200° C. for 8 hours(28,800 s) under 1000 psi (6895 kPa) pressure to give a composite withresin content of 33 weight percent loading. This composite had a Tg of210° C.

EXAMPLE 7 Example of Polyindanylpyridine/Bismaleimide Copolymer as aComposite

The prepreg mat formed in Preparation VII was B-staged in a vacuum ovenat 170° C. under full vacuum for 20 minutes (1200 s) to remove thesolvent. The B-staged material was then pressed at 180° C. for 1 hour(3600 s) and 190° C. for 5 hours (18,000 s) under 1000 psi (6895 kPa)pressure to give a composite with resin content of 44 weight percentloading. This composite had a Tg of 222° C.

We claim:
 1. A thermosettable polymer or prepolymer prepared by reacting(A) a heterocyclic material containing at least one aromatic ring andone heterocyclic nitrogen atom therein or mixture of any two or more ofsuch materials having at least one reactive substituent group having atleast one reactive hydrogen atom attached to a carbon atom attached tothe ring with the proviso that at least one of such heterocyclicmaterials has at least two reactive substituent groups having at leastone reactive hydrogen atom attached to a carbon atom attached to thering; (B) at least one dicarboxylic acid monoanhydride; (C) at least onetetracarboxylic acid dianhydride; wherein the reactants are employed inquantities which provide a mole ratio of (A) to (B) to (C) of from about0.25:1:0.1 to about 4:1:4.
 2. A thermosettable polymer or prepolymer ofclaim 1 wherein said reactive substituent groups are methyl groups andthe reactants are employed in a mole ratio of (A) to (B) to (C) of fromabout 0.8:1:0.5 to about 3:1:2.
 3. A thermosettable polymer orprepolymer of claim 2 wherein in component (A) the heterocyclic moietyis a pyridine moiety, component (B) is represented by the formula##STR12## wherein R is a divalent cycloaliphatic or aromatic group andcomponent (C) is represented by the formula ##STR13## wherein R is atetravalent cycloaliphatic or aromatic group.
 4. A thermosettablepolymer or prepolymer of claim 3 wherein component (A) is2,4,6-trimethylpyridine and component (B) is phthalic anhydride andcomponent (C) is pyromellitic dianhydride.
 5. A process for preparing athermosettable polymer having a softening temperature less than about300° C. which comprises(I) reacting in the absence of a catalyst or adehydration agent a composition comprising(A) a heterocyclic materialcontaining at least one aromatic ring and one heterocyclic nitrogen atomtherein or mixture of any two or more of such materials having at leastone reactive substituent group having at least one reactive hydrogenatom attached to a carbon atom attached to the ring with the provisothat at least one of such heterocyclic materials has at least tworeactive substituent groups having at least one reactive hydrogen atomattached to a carbon atom attached to the ring; (B) at least onedicarboxylic acid monoanhydride; (C) at least one tetracarboxylic aciddianhydride;wherein the reactants are employed in quantities whichprovide a mole ratio of (A) to (B) to (C) of from about 0.25:1:0.1 toabout 4:1:4; (II) stopping the reaction to prevent the formation of highmolecular weight polymer; and (III) subjecting the polymer tosublimation, distillation or solvent extraction to remove unreactedreactants and solvent if employed.
 6. A process of claim 5 wherein saidreactive substituent groups are methyl groups and the reactants areemployed in a mole ratio of (A) to (B) to (C) of from about 0.8:1:0.5 toabout 3:1:2.
 7. A process of claim 6 wherein in component (A) theheterocyclic moiety is a pyridine moiety, component (B) is representedby the formula ##STR14## wherein R is a divalent cycloaliphatic oraromatic group and component (C) is represented by the formula ##STR15##wherein R is a tetravalent cycloaliphatic or aromatic group.
 8. Aprocess of claim 7 wherein component (A) is 2,4,6-trimethylpyridine andcomponent (B) is phthalic anhydride and component (C) is pyromelliticdianhydride.